Multi-lumen catheters are commonly used for extracorporeal procedures in which blood is removed from the vascular system through an aspiration lumen, treated and returned to circulation through an infusion lumen. Apheresis is one example an extracorporeal procedure in which a patient's blood is removed from the vascular system, passed through a machine that removes specific blood components (e.g., plasma, red blood cells, white blood cells and/or platelets etc.) and then returned to circulation. Apheresis procedures generally last from one to four hours, although these times may vary depending on the procedure being performed, the medical condition being treated, the size of the patient and the type of machine being used. The number of treatments also varies based on the procedure being performed. Some procedures, such as red blood cell exchange, are only performed once. In other situations the patient is re-evaluated after two or three procedures to determine if they are responding to the treatment. Certain diseases require a pre-set treatment schedule that may include, for example, five procedures over the course of two weeks. Other procedures require the patient to follow a routine schedule of treatment that may vary from multiple times per week to once per month. Examples of apheresis procedures that require frequent treatments include plasma exchange (e.g., the removal of harmful substances from the blood plasma and subsequent replacement with saline, normal serum albumin or fresh frozen plasma); low density lipoprotein (LDL) apheresis (e.g., to treat familial hypercholesterolemia); photopheresis (e.g., to treat graft-versus-host disease; cutaneous T-cell lymphoma; or heart transplant rejection); allo- and autoantibody removal (e.g., to treat autoimmune disease; hemophilia; or transplant rejection); leukocytapheresis (e.g., to remove malignant white blood cells in leukemia) and thrombocytapheresis (e.g., to treat essential thrombocythemia; or polycythemia vera). Hemodialysis is another example of an extracorporeal procedure in which waste products, such as creatinine, urea, potassium, phosphate and/or free water, are removed from the blood of a patient whose kidneys are in a state of renal failure. In general, hemodialysis treatments are required once a patient has lost 85 to 90 percent of their kidney function. A typical treatment schedule requires performing hemodialysis 3 times a week, although patients who have retained substantial residual kidney function might only require sessions twice-a-week. Larger patients, or patients who have difficulties with fluid overload, may require four hemodialysis sessions per week are often prescribed for larger patients. Short daily home hemodialysis treatments may be performed as frequently as five to seven times per week. While both procedures require the continued re-circulation of blood through an external apparatus, the flow rates required for hemodialysis generally exceed those required for apheresis. For example, hemodialysis typically requires flow rates in the range 300-400 ml/min, but can sometimes exceed 800 ml/min. By contrast, the flow rates required for apheresis procedures can range from 30-60 ml/min (e.g., red blood cell exchange) to 150 ml/min (e.g., plasma exchange).
Medical professionals often prefer the use of implantable ports over peripherally inserted central catheters (i.e., PICCs) for procedures such as apheresis and hemodialysis that require repeated and/or prolonged access to the vascular system. One advantage of implantable ports is that they are completely indwelling, and therefore minimize the risk of infection, especially in patients requiring chronic care. Implantable ports are also more amenable to patients with active lifestyles since their relatively low profile allows them to be easily hidden from view. Ports are typically implanted in the patient's chest and connected to a catheter having a distal tip positioned at the point of treatment. For example, for many medical procedures the catheter tip is positioned at the junction of the superior vena cava and the right atrium. Implantable ports generally include a reservoir (i.e., chamber) in fluid communication with a catheter. The reservoir is typically covered by a needle-penetrable and self-sealing elastomeric septum. The self-sealing septum allows the reservoir to be accessed by puncturing both the patient's skin and the septum with a needle, for example, to infuse and/or aspirate fluid to and from the distal tip of the catheter.
For medical procedures that require multi-lumen access to the vascular system it is common for two ports to be implanted within the patient. While a variety of arrangements are possible, it is most common for one port to be implanted within the patient's left arm and the other port implanted within the right arm. In addition to the increased cost associated with implanting two ports, the separate invasive procedures dramatically increases patient discomfort and the likelihood of negative outcomes such as infection. These problems may be avoided by implanting a multi-reservoir port, which allows the administration of fluid through one reservoir and aspiration of fluid through a separate reservoir. While multi-reservoir ports are more cost-efficient, minimize patient discomfort and decrease patient exposure, they do have drawbacks.
Since fluid flows through a conventional multi-reservoir port (including the catheter) as a continuous stream, it is important that pressure on the aspiration side remains equal (i.e., balanced) to the pressure on the infusion side. With the power source for fluid flow provided by the apheresis or hemodialysis machine, fluid is essentially pulled through the aspiration side under negative pressure and pushed through the infusion side under positive pressure. This requires fluid on the aspiration side to travel a greater distance to reach the power source than fluid on the infusion side, resulting in the formation of high intraluminal negative pressures. These negative pressures force the lumen of the aspiration catheter to collapse or constrict, thereby restricting the flow of fluid throughout the entire system. To avoid harming the patient, automated apheresis and hemodialysis machines are designed to set-off pressure alarms when high intraluminal pressure is detected.
To maintain the proper pressure balance within multi-reservoir port systems, medical professionals typically access the aspiration reservoir of conventional multi-reservoir port systems with a 16 gauge needle. The large inner diameter of the 16 gauge needle is preferred over smaller 18 or 19 gauge needles because they allow fluid to flow into the aspiration reservoir under minimal pressure such that pressure alarms are not set-off. Due to its large inner diameter, a trocar is inserted into the lumen of the 16 gauge needle to prevent coring of the elastomeric septum covering the aspiration reservoir. Unfortunately, the size and shape of standard 16 gauge trocar needles creates large puncture sites within the elastomeric septum. Repeated overlapping punctures by the 16 gauge trocar eventually result in the formation of leakage sites within the septum, ultimately rendering the port unsuitable for safe and reliable use.
As evidenced by the competing interests of maintaining septum integrity and avoiding high intraluminal negative pressure, there is a continuing need for multi-reservoir port and non-coring needle systems that support high-flow applications with minimal impact on the puncture life of the elastomeric septum.